She's just dikkin' with ya, CD. Trying not to give you the satisfaction of knowing that her infidelitus was interruptus.
I wouldn't have a "speech" with her until you're ready to be able to preface everything with "I have decided -- ." I would spend the week getting your ducks in a row, and -- frankly -- just GAL. Don't give HER the satisfaction of thinking you're sitting around moping over her, and pining over what she did.
Remember, the "default" position in your marital dynamic has shifted dramatically this weekend, from you WONDERING if she's having an affair/ACCUSING her of having one, to SHE'S HAVING AN AFFAIR.
SHE WAS BUSTED.
YOU BUSTED HER SORRY ASS.
The way I see it, the burden's on HER if she wants you -- or anyone else in her life (her mother, her aunt, her friends, and even her grown daughter one day) -- to believe that she DIDN'T break up her family thru adultery.